1. Field of the Invention
The present invention relates to a substrate thermal processing apparatus for processing a substrate.
2. Description of the Background Art
During processing of a substrate such as a semiconductor wafer, a glass substrate for photomask, a glass substrate for liquid crystal display and a substrate for optical disk, a substrate thermal processing apparatus, e.g., a substrate heating apparatus which heats up a substrate which seats a resist film to a predetermined temperature, and a substrate cooling apparatus which cools the heated substrate down to a predetermined temperature, are used.
FIG. 7 is a schematic diagram showing a principal portion of a conventional substrate heating apparatus. In FIG. 7, the substrate heating apparatus comprises a heating plate 1 for heating up a substrate W to a predetermined temperature. Inside the heating plate 1, a heat source such as a mica heater is buried. Further, a plurality of ball-like shaped spacers 5 for supporting a substrate W at a bottom surface of the substrate W are disposed in a top surface of the heating plate 1.
Disposed below the heating plate 1 are three elevating pins 3 and an elevating frame 6 which is linked to the elevating pins 3. A cylinder 7 is linked to one end of the elevating frame 6, so that a substrate W is moved upward and downward by the three elevating pins 3 as a rod of the cylinder 7 expands and contracts.
The substrate heating apparatus as described above is used for heating processing prior to exposure of, for example, a resist film which is formed on a substrate (prebake processing), heating processing after exposure (PEB: Post Exposure Bake), heating processing after developing (postbake processing), etc. An external substrate transport device supplies substrates W sequentially to the substrate heating apparatus at constant time intervals.
FIG. 8 is a view showing a heat history of a substrate in the substrate heating apparatus which is shown in FIG. 7. In FIG. 8, as a substrate W on which a resist film is formed is mounted on the heating plate 1 which is disposed within the substrate heating apparatus, the temperature of the substrate W is increased to a predetermined set temperature T1, e.g., 110.degree. C., from around a room temperature. The substrate W is thereafter maintained at the set temperature T1 during a predetermined heating processing period, and is taken out to outside after a certain standby period.
Recent years have seen use of various types of resists in accordance with characteristics of patterns which are formed on a substrate W. The set temperature T1 of a substrate W in a thermal processing in the substrate heating apparatus is different depending on the type of a resist. Hence, where substrates W which are coated with different types of resists are supplied successively, it is desired to change the set temperature T1 for a supplied substrate W instantly in accordance with the type of a resist of the supplied substrate W before heating the substrate W.
In the conventional substrate heating apparatus, an output from the heat source, such as a mica heater, which is disposed within the heating plate 1 is controlled so as to adjust the set temperature T1. Therefore, when the set temperature T1 for the next substrate W is lower than the set temperature T1 for the immediately preceding substrate W, it is necessary to control an output from the heat source of the heating plate 1 to thereby decrease a surface temperature of the heating plate 1.
However, the heating plate 1 does not comprise cooling means. Because of this, natural heat radiation is the only way to decrease the temperature of the heating plate 1. Contradicting this, since the substrate heating apparatus is internally kept at a high temperature, a coding effect of natural heat radiation is extremely small. Hence, the surface temperature of the heating plate 1 does not decrease easily, which makes it difficult to successively process substrates W for which the set temperature T1 is different.
Against this background, a plurality of substrate heating apparatuses are disposed, corresponding to the types of the set temperature T1 for substrates W, for the purpose of heating processing. This requires a number of substrate heating apparatuses and pushes up a facilities cost.